Boiler and Method for Operating a Boiler

ABSTRACT

The invention relates to a boiler and to a method for operating a boiler. To effectively prevent damage to the boiler wall, in particular by corrosion, the flow speed characteristic of a furnace floor flow running horizontally to the furnace floor is determined, a source region of the horizontal furnace wall flow on at least one furnace wall is determined and an insulating gas is supplied to the source region of the horizontal furnace wall flow, in such a way that an insulating gas layer, which insulates the respective boiler wall from the flue gas, is created by the horizontal extension of the insulating gas with the aid of the furnace wall flow.

The invention relates to a steam generating boiler and to a method for operating a steam generating boiler.

In boilers with linear or tangential firing two gas flows are generated which in addition to the axially orientated flow components include radially orientated flow components. These radially orientated flow components may be caused both by different pressure conditions in the boiler space as well as by mutual influences of the flow paths of mutually opposite burners with simultaneous influences of the circulation regions in the combustion chamber and bring about a greater or lesser flue gas flow towards the side walls of the boiler vessel including fuel products which are still in part capable of reacting.

A result of this is the formation of regions of oxygen starvation which due to geometrical conditions spread out preferentially towards the center of the boiler walls but which, caused by pressure differences, may frequently change their positions and in the long term result in damage to material due to corrosion of the pipe walls. The phenomenon of the formation of such oxygen starvation regions will in the following be elucidated with reference to the diagrammatic illustrations in FIG. 10 and FIG. 11.

FIG. 10 shows diagrammatically a combustion chamber 1 of a boiler operated by way of linear or boxer firing and defined by a front wall 2, a rear wall 3 and side walls 4 and 5 in side elevation (FIG. 10 a) respectively in sectionalized view along the line A-A (FIG. 10 b). Along the front wall 2 and the rear wall 3, a plurality of mutually opposite burners (symbolized by the arrows 6 and 7 respectively) are arranged at a uniform level in one or more mutually opposing burner planes. The burner flows, symbolized by lines 8, meet in this arrangement in the central region of the combustion chamber in such a manner that a resultant flow is formed in the direction of the side walls 4 and 5, whereby oxygen starvation regions are formed in the regions 9 and 10 illustrated in broken lines.

A quantitative illustration of the above described conditions involving the formation of oxygen starvation regions in a combustion chamber operated by means of linear or boxer firing is illustrated in FIG. 11, regions of different oxygen concentrations in the combustion chamber each being represented by different shades of gray; the scale shown on the left hand side of the illustration indicates for each shade of gray the associated mass content of oxygen.

FIG. 12 illustrates diagrammatically a combustion chamber 11 of a boiler operated by way of corner or tangential firing and outlined by a front wall 12, a rear wall 13 and side walls 14 and 15 in side elevation (FIG. 12 a) respectively in a sectionalized view along the line B-B (FIG. 12 b). In the four corner regions of the boiler body, at a uniform level thereof, a plurality of burners, (symbolized by the arrows 16-19) are arranged in one or more superimposed burner planes to form a corner firing system. The burner flows symbolized by lines 20 are forced by the ever increasing degree of filling in the combustion chamber 11 against the front wall 12, the rear wall 13 and the side walls 14 and 15, particularly in the higher lying regions whereby in the regions 21-24 indicated in broken lines oxygen starvation regions are formed.

For the avoidance of oxygen starvation regions and thereby for protection against corrosive attack it is known to integrate wall air nozzles into burner groups (e.g. in the case of tangential firing) by way of which a partial air flow, deflected from the burner flow axis is conducted in the direction of the combustion chamber wall. Furthermore, it is known to install lateral air nozzles besides burners close to the wall by way of which an air flow is injected at high velocity parallel to the burner flow axis into the combustion chamber in the immediate vicinity of the wall. However, these expedients suffer from the disadvantage that, on the one hand by the high ejection velocity of the air flow introduced from the side air nozzles new vortexes are formed which conduct the oxygen depleted flue gas towards the boiler walls and that on the other hand frequently the depth of penetration of these air flows into the more viscous flue gas flow is inadequate such that an oxygen enrichment in the endangered boiler regions cannot be attained, which has been simulated in numerous experiments with variations of the side and burner air quantities in a variety of boiler installations and in numerous simulation models.

By way of example in FIG. 13 the calculated simulation results for an oxygen concentration array with an arrangement of side air nozzles 31 arranged adjoining the burners 30 are shown. Regions of different oxygen concentrations in the combustion chamber are respectively illustrated by different shades of grayness, the scale which in the drawing is shown on the left hand side indicating the oxygen mass proportion associated with each shade of grayness. As is apparent from the simulation no effective oxygen enrichment is attained in the side wall region 32 to be protected. An increased transport into the side wall region 32 to be protected can only be brought about when employing larger amounts of air, which is disadvantageous or not acceptable both for reasons of economy as well as from a thermal and emission technology point of view.

From WO 98/16779 it is known to fit wall air nozzles in the endangered combustion chamber side walls in order to protect the side walls against corrosion. These wall air nozzles are arranged in one or more horizontal rows or in an arcuate pattern over the entire wall width in order to form on the side walls a corrosion protective layer in the combustion chamber flow by means of the wall air fed into the wall air nozzles and by utilizing vertical flow components.

These expedients as well suffer from the drawback, however, that viewed over the height covered by the string of burners and, where applicable, between the plurality of horizontal nozzle rows, regions of oxygen starvation are still formed. This is apparent from the illustration according to FIG. 14 of simulation results, the scale shown in the illustration on the left hand side once again indicating for each shade of grayness the associated oxygen mass content. The burners are denoted in this illustration by the reference number 40, the horizontal rows of nozzles by 41. As is apparent from the simulation results an oxygen starvation region 42 is formed between the horizontal nozzle rows 41. With such an arrangement as well the side walls are accordingly still subject to damage due to corrosion.

To summarize, according to known attempts at creating a corrosion protection, wall air nozzles are integrated either as side air nozzles adjoining the burners (e.g. in the case of tangential firing) or integrated into one or more essentially horizontal rows on the side walls (which are not equipped with burners). Any corrosion protection in those arrangements is either inadequate or can only be attained employing amounts of wall air which for economic as well as thermal and emission technological reasons are unacceptable.

It is accordingly an object of the present invention to provide a steam generating boiler and a process for operating a steam generating boiler by means of which damage to the boiler wall in particular by corrosion is effectively avoided.

This object is attained according to the features of the independent patent claims.

A method according to the invention for operating a steam generating boiler in which a combustion chamber defined by boiler walls is fired by combustion of fuel causing the formation of a flue gas flow by means of a plurality of burners, includes the following steps:

-   -   determining the flow velocity characteristics of a basic         combustion chamber flow which in relation to the bottom of the         combustion chamber is horizontal;     -   identifying a source region of the horizontal combustion chamber         wall flow on at least one boiler wall which is not equipped with         burners; and     -   feeding an insulating gas into the source region of the         horizontal combustion chamber wall flow, such that by horizontal         expansion of the insulating gas by means of the combustion         chamber basic flow an insulating gas layer is formed which         insulates the respective boiler wall from the flue gas flow.

The present invention is based on the realization that when firing a steam generating boiler the flow component which in relation to the combustion chamber bottom is horizontal, particularly in the region of the string of burners, dominates as compared with the vertical component. Due to the feeding of the insulating gas according to the invention (e.g. the wall air) in the source region of this horizontal component of the combustion chamber basic flow along the combustion chamber wall, this flow is effectively utilized for distributing the insulating gas along the combustion chamber wall to be protected, so that the formation of oxygen starvation regions and of resultant corrosion is effectively counteracted.

Within the meaning of the invention, the expression “insulating gas layer” is to be understood to denote a gas layer which in relation to the flue gas flow exhibits a feed impulse flow into the combustion chamber so low that, due to the lack of mixing energy in the insulating gas layer, a mixing of the insulating gas layer with the flue gas either does not take place at all or in any event with so much delay that compared with the flue gas flow present in the immediate vicinity of the boiler wall region a protective layer is formed which counteracts the effects on the atmosphere in the immediate vicinity of the boiler wall and which accordingly, in this sense, “insulates” the boiler wall region against the flue gas flow.

The term “source region” within the meaning of the invention denotes a region from which the respective wall flow or its horizontal component respectively issues and in which the resultant flow velocity amounts essentially to zero.

According to a preferred embodiment the feeding of the insulating gas proceeds by way of a gas feed nozzle arrangement provided in at least one combustion chamber wall which in each of a plurality of mutually adjoining planes, horizontal in respect of the bottom of the combustion chamber, includes exactly one gas feed zone which is arranged in the source region above the horizontal component of the combustion chamber wall flow associated with this plane.

The combustion chamber may comprise a symmetrical burner arrangement and the gas feed nozzles may be arranged in a line vertical in relation to the respective combustion chamber wall and extending along the vertical center line of the respective combustion chamber wall.

Preferably the gas feed nozzle arrangement extends essentially along the burner string level of the combustion chamber.

According to an alternative embodiment the combustion chamber includes an intermediate wall between opposite walls of the boiler and the gas feed nozzles provided in the source region of the combustion chamber flow are provided in the intermediate wall.

According to a preferred embodiment the feeding of the insulating gas proceeds by way of a gas feed slot, vertical in relation to the combustion chamber bottom provided on at least one combustion chamber wall and extending more or less continuously essentially along the level of the burner string.

Preferably air is used as the insulating gas which is fed from the combustion gas supply of the combustion chamber.

The content by volume of the air used as the insulating gas preferably amounts to maximally 10% more preferably maximally 5% of the total amount of air required for the conversion of the fuel.

It is also possible to employ an oxidizing gas or an inert gas as the insulating gas.

According to a preferred embodiment the insulating gas flow is generated independently in individual sectors of the boiler wall so that variations in the strength of the flue gas flows which may arise in the boiler wall sectors due to geometrical circumstances and the arising pressure differences may, depending on conditions prevailing in the respective sector, may be taken into account by a locality dependent variation of the insulating gas flow.

According to a preferred embodiment the steam generating boiler includes analysis means for the determination of contents by volume of flue gas components in the gas atmosphere prevailing, adjoining the boiler wall, and a regulating means for regulating the insulating gas flow as a function of the volume proportions so determined. The flue gas components so determined include preferably oxygen and carbon monoxide but may also, depending on requirements, include further flue gas components, in particular HCl and/or H₂S.

The determination of proportions by volume of the flue gas components and/or regulating the insulating gas flow in this context is preferably performable independently from one another in individual sectors of the boiler wall.

According to a preferred embodiment the determination of the volume proportions of the flue gas components and/or the regulating of the insulating gas flow can be performed repeatedly in independent measuring cycles. In this manner it becomes possible to take into account variations in time of the conditions prevailing on the boiler wall surface or in the individual boiler wall sectors by appropriately regulating the insulating gas flow, whereby the protection attained according to the invention against damage of the boiler wall by corrosion is improved even further.

According to a preferred embodiment the insulating gas flow is fed from the combustion gas supply of the combustion chamber which thereby attains a dual functionality.

According to a preferred embodiment the gas feed means in each boiler wall sector includes a gas feed unit (e.g. air box) for the feeding of insulating gas to the surface of the boiler wall into the combustion chamber.

Preferably in this context the gas feed units associated with a boiler wall are each connected to a main line coupled separately to the combustion gas supply. Preferably in this context each main line includes a regulating element for regulating the gas flow there through so that a selective feed to the individual boiler walls can take place by way of the associated main line.

According to a preferred embodiment each gas feed unit is moreover adapted to be selectively coupled by way of a closure element to the associated main line so that also a selective feed to the individual boiler wall sectors can take place.

Preferably in this context the regulating element of the particular main line and/or the closure element of the respective air box is operated as a function of the volume ratios of flue gas components determined in the gas atmosphere adjoining the boiler wall.

In this context the burners may more particularly be arranged both for linear firing as well as for tangential firing of the combustion chamber.

A steam generating boiler according to the present invention includes:

-   -   a combustion chamber defined by boiler walls;     -   a plurality of burners for firing the combustion chamber by         means of fuel combustion with the formation of a flow of flue         gas; and     -   a gas feed device for feeding an insulating gas; wherein the gas         feed device is so arranged in the source region of a horizontal         combustion chamber flow on at least one boiler wall, that by         horizontal expansion of the introduced insulating gas due to the         combustion chamber basic flow an insulating gas layer insulating         the respective boiler wall from the flue gas flow can be         generated.

Further embodiments of the invention may be derived from the following description and the subsidiary claims.

In what follows the invention will be further elucidated with reference to a working example illustrated in the accompanying illustrations.

There is shown in:

FIG. 1 in a horizontal section of the combustion chamber a velocity vector array calculated according to the invention for horizontal combustion chamber flows;

FIG. 2 in addition to the illustration of FIG. 1 (lower portion) an oxygen concentration array (upper portion) calculated according to the invention.

FIG. 3 a diagrammatic perspective partial view of a combustion chamber including a vertical row of nozzles arranged in a side wall region according to a preferred embodiment of the present invention, wherein the calculated oxygen concentration (mass proportions) is illustrated.

FIG. 4 in a horizontal section of the combustion chamber according to the embodiment of FIG. 3 a calculated oxygen concentration array (top) and a velocity vector array (bottom);

FIG. 5 a diagrammatic side view in section of a combustion chamber for illustrating a nozzle arrangement according to a further embodiment of the invention;

FIG. 6 a diagrammatic side elevation in section of a combustion chamber for illustrating a nozzle arrangement according to a further embodiment of the invention;

FIG. 7 a diagrammatic sketch in side elevation for illustrating the system according to the invention in accordance with a preferred embodiment for a boiler with boxer firing;

FIG. 8 a sectional view corresponding to FIG. 7 along the line A-A;

FIG. 9 an enlarged diagrammatic sketch in side elevation of a detail from FIGS. 7-8 for elucidating the manner of functioning of the system according to the invention according to the preferred embodiment of FIGS. 7-8;

FIG. 10 a diagrammatic view of the design of a combustion chamber with boxer or linear firing in a steam generating boiler according to the state-of-the-art in side view elevation (FIG. 4 a) and in section respectively along the line A-A (FIG. 4 b); and

FIG. 11 an illustration of the calculated oxygen concentration in the wall region of a combustion chamber without wall air feed according to the state-of-the-art;

FIG. 12 a diagrammatic view of the design of a combustion chamber with corner or tangential firing in a steam generating boiler according to the state-of-the-art in side elevation (FIG. 5 a) and in section respectively along the line A-A (FIG. 5 b).

FIG. 13 in a horizontal section of a combustion chamber a calculated oxygen concentration array (top) as well as a velocity vector array (bottom) for a nozzle arrangement according to the state-of-the-art; and

FIG. 14 a diagrammatic perspective partial elevation of a combustion chamber including an illustration of the calculated oxygen concentration array for a further nozzle arrangement according to the state-of-the-art.

According to the invention, for the distribution of an insulating gas flow in the combustion chamber region to be protected, flow conditions are utilized which are characterized in that along the side walls to be protected of the combustion chamber a horizontal basic flow exists. For this basic flow which is horizontal in relation to the bottom of the combustion chamber there exists along the side walls a “source region” starting from where the horizontal expansion of the flow in the direction of the corners of the combustion chamber proceeds. This situation is illustrated in FIG. 1, wherein in horizontal section through a combustion chamber the combustion chamber flows are given on the basis of calculated velocity vectors. Different magnitudes of the flow velocity are each illustrated with different shades of grayness, the scale shown on the left hand side of the drawing indicating the magnitude of the flow velocity (in units of m/s) associated with each shade of grayness. The burners in that illustration are designated by the reference number 50 and the source region of the horizontal component of the basic flow is denoted as 51 or 52 respectively. The horizontal component of the basic flow is symbolized by the arrows 53.

In FIG. 2 (upper portion) the formation of an oxygen starvation region is illustrated in addition, subject to the condition that in the starting situation according to FIG. 1 no protective measures whatsoever have been taken.

From the simulation illustrated in FIG. 1 it is possible in accordance with the invention to determine in the immediate vicinity of each side wall of the combustion chamber (not equipped with burners 50) a source region 51, 52 of the horizontal basic flow along the respective side wall, starting from where the horizontal flow (according to FIG. 1 to the left and to the right along the indicated arrows) and in which the resulting flow velocity is essentially zero. More accurately each plane which is horizontal in relation to the bottom of the combustion chamber has associated therewith a source point (being the starting point of the horizontal flow component prevailing in that plane) all source points of different horizontal planes together forming the source region for the horizontal basic flow along the respective side wall.

The source points constituting the source region accordingly form an array extending in vertical direction (in particular along the so-called burner string) which in a final analysis depends on the specific parameters (combustion chamber geometry, arrangement of side as well as possible intermediate walls, burner array, burner operation etc.) and which according to the process according to the invention is determined first.

The detection according to the invention of the source region of a horizontal base flow can be performed either according to FIG. 1 and FIG. 2 by simulation e.g. by means of numeric CFD modeling (CFD=“computational fluids dynamics”) of the flow conditions in the combustion chamber based on basic parameters of the burners used, dimensions etc., or alternatively experimentally (by way of an appropriate sensor system provided in the combustion chamber region).

Once according to the invention, as described above, the source region of the horizontal basic flow has been determined, a nozzle system is provided in each side wall of the combustion chamber such that the wall air nozzles are each provided in the source region as determined above. Thus, for example, in the working example as shown in FIG. 3 including a symmetrical configuration of the combustion chamber, the wall air nozzles are arranged in a vertical row of nozzles 61 extending along the side wall (not equipped with burners 60) along the vertical center line. The row of nozzles 61 in this context preferably extends at least along the level of the string of burners.

In FIG. 4 the oxygen concentration area (upper view) resulting from the nozzle arrangement of FIG. 3 according to the invention as well as the flow conditions being created (lower illustration) are illustrated. From these characteristics of oxygen concentration obtained by means of simulation and the flow velocity vectors it becomes apparent that due to the injection according to the invention of air in the source region 62, 63 of the horizontal wall flow an effective expansion of the insulating air takes place along the side walls to be protected, the horizontal wall flow in the combustion chamber being employed as a transport medium.

As appears from FIGS. 5 and 6, depending on the geometry of the combustion chamber and the arrangement of the side walls and any possible intermediate walls, different constructional designs of the wall air nozzles are employed according to the invention. In particular FIG. 5 shows a nozzle arrangement along an inner double intermediate wall 71 which sub-divides the combustion chamber into two partial chambers with identical burner arrangements 70. According to this working example pairs of slotted nozzles 72, likewise lie in vertical arrangement, however, with slots 72 to the left and to the right of a non-accessible connecting plane of the double wall, are provided, the slot-shaped nozzles being supplied with air or insulating gas by way of horizontal feed lines, diagrammatically illustrated, accommodated in the cavity of the double intermediate wall.

Along the outer combustion chamber walls it is for example also possible to select the more simple arrangement illustrated in FIG. 6, wherein a plurality of wall air nozzles 81 arranged in a vertical row is supplied with air or insulating gas by way of a feed line 81 extending vertically along the combustion chamber wall.

The spacing and the aperture size of the wall air nozzles in the vertical nozzle arrangement according to the invention may be selected appropriately as a function of the static conditions. In this context the insulating gas protective layer is as a rule generated with increasing effectiveness, the closer is the spacing of adjoining wall air nozzles, i.e. the more effectively the respective wall surface is fed with insulating gas in the source region of the horizontal wall flow. In principle therefore when designing the vertical nozzle arrangement—depending on the concrete design and construction limitations—the ideal of a continuous vertical slot in the source region of the horizontal wall flow should be aimed at as far as possible.

In the following a preferred embodiment of the invention will be elucidated in which the insulating gas flow can be regulated in individual boiler wall sectors independently from one another and in dependency of the conditions actually prevailing there.

The nozzle arrangement according to the invention proceeds not necessarily along a straight vertical line, because the configuration in the source region of the horizontal wall flow may also follow a non-linear pattern depending on the concrete flow conditions in which in the vertical direction adjoining nozzles are in horizontally staggered mutual interrelationship in order each to optimally utilize the prevailing horizontal wall flow.

FIG. 7 and FIG. 8 show a diagrammatic sketch to illustrate the design and mode of function of a steam generating boiler with boxer firing according to the invention in accordance with a preferred embodiment, more particularly according to FIG. 7 in side elevation and according to FIG. 8 in sectional view (along the line A-A of FIG. 7).

In accordance with FIG. 7 a combustion chamber 100 of a steam generating boiler is defined by a boiler wall including a front wall 101, a rear wall 102 and side walls 103 and 104. Along the front wall 101 and the rear wall 102 in each case a plurality of burners are arranged, at the same level mutually opposite in pairs as well as in a plurality (three in accordance with the working example) of burner planes one above the other to form a linear or boxer firing arrangement, the burners being symbolized by the arrows 105 and 106 respectively. The burner flows symbolized by lines 107 meet in the center of the combustion chamber in such a manner that a resultant flow is formed in the direction of the side walls 103 and 104, whereby in the absence of appropriate counter measures areas of oxygen starvation are formed in the regions 108 and 109 represented by broken lines along the side walls 103 and 104.

The steam generating boiler according to the invention in accordance with the illustrated working example moreover includes a plurality (six in the working example) of air boxes 109-114, each air box 109-114 being individually associated with one boiler wall region sector each. By means of each such air box the insulating air is fed as explained above into the previously determined source region of the horizontal component of the combustion chamber flow.

The air boxes 109-114 according to the illustrated preferred embodiment provided along a side wall 103 or 104 respectively are each individually connected by way of an associated individual duct 115-120 to a common main duct 121 or 122, each main duct 121 or 122 respectively providing air to an entire boiler side wall 103 and 104 respectively. The main ducts 121 and 122 are jointly connected to a combustion gas supply system 123 by means of which the air boxes 109-114 as well as the burners are supplied with air. The respective air flow is represented by broken lines drawn alongside the ducts.

Each of the individual ducts 115-120 includes a closure element 124 by means of which when required the air supply of the particular air box can be switched on or off. Furthermore, each main duct 121 or 122 respectively includes a regulator element 125 for regulating the amount of air flowing through the respective main duct, which in turn is quantitatively determined by a measuring device 126 connected upstream or downstream of a regulating element 125.

Each of the air boxes 109-114 includes a plurality (eight each in accordance with the working example) of gas withdrawal localities 127, each gas withdrawal locality 127 being individually connected by way of a measuring duct 128 to a measuring point reversing device 129. From the measuring point reversing device 129 the gas withdrawn is passed to an analyzer 130 which sucks in the gas from the region of the combustion chamber 100 close to the wall by way of the above described route and analyses the composition of the atmosphere in the respective boiler wall region. The analyzer 130 is preferably designed for the determination of proportions by volume of (O₂) and carbon monoxide (CO), but may in addition and as required also be suitable for the determination of the contents by volume of further flue gas components such as HCl or H₂S.

The respectively measured volumetric proportions (in particular oxygen and carbon monoxide proportions) in the atmosphere of the particular boiler wall region measured in any particular run (measuring cycle) are stored in the memory of a evaluation unit 131 and compared with predetermined index values, whereafter the evaluation unit 131 issues an appropriate output signal according to which the closure element 124 in the individual duct 115-120 associated with the corresponding air box 109-114, is actuated. Preferably in doing so the corresponding closure element for increasing the insulating gas feed flow to the respective air box 109-114 is actuated whenever the determined oxygen content by volume decreases or whenever the determined content by volume of carbon monoxide (or HCl or H₂S) increases.

Simultaneously, as apparent from FIG. 9, the output signal of the evaluation unit 131 is passed on to an index value adjuster 132 which presets the index value for the adjustment (by means of adjustment element 125 and measuring device 126) of the amount of air which flows through the respective main duct 121 or 122 respectively. On the basis of the output signal of the evaluation unit 131 and the positional signal of the closure element 124 a recalculation of the air index value for the entire side wall of the boiler takes place in the index value adjuster 132. The air feed index value is compared with the air flow measured in the measuring device 126 and the flow through the respective main duct 121 or 122 respectively is adjusted by means of a regulator 133 by way of the regulating element 125, more particularly such that the throughput to the respective boiler wall is increased whenever the volume ratio of oxygen determined for this overall boiler wall decreases, or whenever the volume ratio of carbon monoxide (or HCl or H₂S), determined for this overall boiler wall, increases.

After the conclusion of a measuring cycle within any one sector of a boiler wall region the stored measuring data are deleted and the cycle of locality dependent measurements of the atmosphere of the boiler wall region at successive measuring points 127, corresponding actuation of closure elements 124 in the individual ducts 115-120 leading to the respective air boxes 109-114, recalculation of air feed index values for the entire boiler wall and appropriate actuation of the regulating element 125 in the respective main duct 121 or 122 respectively is again resumed.

During the operation of the steam generating boiler according to the invention the air feed rushing in from the combustion gas supply means by way of the main duct and the individual ducts into the air boxes enters approximately in the central region of the boiler wall at a plurality of localities (not illustrated) arranged vertically in the source region of the horizontal component of the combustion chamber wall flow enters at a very low velocity into the combustion chamber and expands utilizing the basic flow of the combustion chamber essentially blanket-like in the area close to the tube wall with the formation of an insulating gas layer. This expansion proceeds at a flow velocity which by comparison with the flue gas flow is so low that a mixing with the flue gas due to the lack of mixing energy in the gas layer proceeds only at a greatly retarded rate, if at all. The oxygen enriched air insulation layer thus formed in the immediate vicinity of the boiler wall region in that manner prevents the formation of oxygen starvation regions in the respectively endangered regions 108 and 109.

In accordance with the above described preferred embodiment a concerted regulation of the protective gas layer formed in the boiler wall region can take place, more particularly both for an entire side wall 103 or 104 outlining the combustion chamber (by regulating the air flow through the main duct 121 or 122) as well as also of the air supply to individual sectors (by way of the respective closure elements 124), the respective index values for regulating in independent measuring cycles being newly fixed on the basis of a repeated locality dependent measurement of the atmosphere in the boiler wall region. In that manner a variation in terms of time and locality of the flow conditions in the combustion chamber and a variation of the oxygen starvation regions resulting there from can be taken into account by appropriately regulating the protective gas layer according to the invention.

Even though the above described selective regulation is advantageous, it is not an absolute precondition for the realization of the invention. In particular, it is also possible to omit the above mentioned measuring and regulating devices and to provide a constant air feed, more particularly either for an entire boiler wall or alternatively with different feed rates in the individual boiler wall region sectors.

The air boxes used with the system according to the invention need not be connected by way of main or individual ducts jointly to the combustion gas supply means. Alternatively, (even though less preferred) it is also possible to provide a supply to the air boxes from a separate air feed system. Moreover, the number of air boxes is optional, such that in particular even a single box only for each wall of the combustion chamber may be provided.

Furthermore, the invention is not limited to the feeding of air for the insulating gas layer. In principle, it is also possible to use a different inert or oxidizing gas mixture which is suitable for corrosion protection.

Even though the invention has been elucidated through the example of a steam generating boiler with boxer firing, it is likewise applicable also to a steam generating boiler with tangential firing.

LIST OF REFERENCE NUMBERS

-   1 Combustion Chamber -   2 Front Wall -   3 Rear Wall -   4 Side Wall -   5 Side Wall -   6 Arrow (burner) -   7 Arrow -   8 Lines (burner flows) -   9 Oxygen Starvation Region -   10 Oxygen Starvation Region -   11 Combustion Chamber -   12 Front Wall -   13 Rear Wall -   14 Side Wall -   15 Side Wall -   16 Arrow (burner) -   17 Arrow -   18 Arrow -   19 Arrow -   20 Lines (burner flows) -   21 Oxygen Starvation Region -   22 Oxygen Starvation Region -   23 Oxygen Starvation Region -   24 Oxygen Starvation Region -   30 Burner -   31 Lateral Air Nozzles -   32 Side Wall Region -   40 Burner -   41 Horizontal Nozzle Row -   42 Oxygen Starvation Region -   50 Burner -   51 Source Region -   52 Source Region -   53 Arrows (basic flow) -   60 Burner -   61 Vertical Nozzle Row -   62 Source Region -   63 Source Region -   70 Burner -   71 Intermediate Wall -   72 Slots -   80 Burner -   81 Wall Air Nozzles -   100 Combustion Chamber -   101 Front Wall -   102 Rear Wall -   103 Side Wall -   104 Side Wall -   105 Arrow (burner) -   106 Arrow -   107 Lines (burner flows) -   108 Oxygen Starvation Region -   109 Air Box -   110 Air Box -   111 Air Box -   112 Air Box -   113 Air Box -   114 Air Box -   115 Individual Duct -   116 Individual Duct -   117 Individual Duct -   118 Individual Duct -   119 Individual Duct -   120 Individual Duct -   121 Main Duct -   122 Main Duct -   123 Combustion Gas Supply -   124 Closing Element -   125 Regulating Element -   126 Measuring Device -   127 Gas Withdrawal Locality -   128 Measuring Duct -   129 Measuring Position Reversing Device -   130 Analyzer -   131 Evaluation Unit -   132 Index Volume Adjustor -   133 Regulator 

1. Method for operating a steam generating boiler in which a combustion chamber (100) defined by boiler walls (101-104) is fired by combustion of fuel causing the formation of a flue gas flow (107) by means of a plurality of burners (105, 106), including the following steps: determining the flow velocity characteristics of a basic combustion chamber flow which in relation to the bottom of the combustion chamber is horizontal; identifying a source region of the horizontal combustion chamber wall flow on at least one boiler wall (103-104); and feeding an insulating gas into the source region of the horizontal combustion chamber wall flow, such that by horizontal expansion of the insulating gas by means of the combustion chamber basic flow an insulating gas layer is formed which insulates the respective boiler wall (103-104) from the flue gas flow (107).
 2. Method according to claim 1, wherein the feeding of the insulating gas proceeds by way of a gas feed nozzle arrangement provided in at least one combustion chamber wall which in each of a plurality of mutually adjoining planes, horizontal in respect of the bottom of the combustion chamber, includes exactly one gas feed zone which is arranged in the source region of the horizontal component of the combustion chamber wall flow associated with this plane.
 3. Method according to claim 2, wherein the gas feed nozzles are arranged in a line vertical in relation to the respective combustion chamber wall and extending along the vertical center line of the respective combustion chamber wall.
 4. Method according to claim 2, wherein the gas feed nozzle arrangement extends essentially along the burner string level of the combustion chamber.
 5. Method according to claim 2, wherein the combustion chamber is divided by an intermediate wall, and wherein the gas feed nozzles provided in the source region of the combustion chamber flow are provided in the intermediate wall.
 6. Method according to claim 1, wherein the feeding of the insulating gas proceeds by way of a gas feed slot, vertical in relation to the combustion chamber bottom provided on at least one combustion chamber wall and extending more or less continuously essentially along the level of the burner string.
 7. Method according to claim 1, wherein air is used as the insulating gas which is fed from the combustion gas supply of the combustion chamber.
 8. Method according to claim 7, wherein the content by volume of the air used as the insulating gas amounts to maximally 10%, preferably maximally 5% of the total amount of air required for the conversion of the fuel.
 9. Method according to claim 1, wherein an oxidizing gas is used as the insulation gas.
 10. Method according to claim 1, wherein an inert gas is used as the insulating gas.
 11. Method according to claim 1, wherein the insulating gas flow is generated independently in individual sections of the boiler wall.
 12. Method according to claim 1 including the further steps of: determining volume proportions of flue gas components in the gas atmosphere present adjoining at least one boiler wall; and regulating the insulating gas flow as a function of the determined proportions of flue gas components.
 13. Method according to claim 12, wherein the determination of proportions by volume of the flue gas components and/or regulating the insulating gas flow is performed independently from one another in individual sectors of the boiler wall.
 14. Method according to claim 13, wherein the determination of the volume proportions of the flue gas components and/or the regulating of the insulating gas flow is performed repeatedly in a plurality of measuring cycles.
 15. Method according to claim 12, wherein the flue gas components include oxygen (O₂) and carbon monoxide (CO).
 16. Method according to claim 12, wherein the flue gas components include also HCl and/or H₂S.
 17. Steam generating boiler, including a combustion chamber (100) defined by boiler walls (101-104); a plurality of burners (105, 106) for firing the combustion chamber (100) by means of fuel combustion with the formation of a flow of flue gas (107); and a gas feed device for feeding an insulating gas; wherein the gas feed device is so arranged in the source region of a horizontal combustion chamber flow on at least one boiler wall, that by horizontal expansion of the introduced insulating gas due to the combustion chamber basic flow an insulating gas layer insulating the respective boiler wall (103-104) from the flue gas flow (107) can be generated.
 18. Steam generating boiler according to claim 17, wherein the gas feed means comprises a gas feed nozzle arrangement provided in at least one combustion chamber wall which in a plurality of mutually adjoining planes horizontal in respect of the bottom of the combustion chamber includes exactly one gas feed zone which is arranged in the source region of the horizontal component of the combustion chamber wall flow associated with this plane.
 19. Steam generating boiler according to claim 18, wherein the gas feed nozzles are arranged in a line vertical in relation to the respective combustion chamber wall and extending along the vertical center line of the respective combustion chamber wall.
 20. Steam generating boiler according to claim 18, wherein the gas feed nozzle arrangement extends at least along the burner string level of the combustion chamber.
 21. Steam generating boiler according to claim 18, wherein the combustion chamber is divided by an intermediate wall and wherein the gas feed nozzles provided in the source region of the combustion chamber flow are provided in the intermediate wall.
 22. Steam generating boiler according to claim 17, wherein the gas feed means comprises a gas feed slot, vertical in relation to the combustion chamber bottom provided on at least one combustion chamber wall and extending more or less continuously essentially along the level of the burner string.
 23. Steam generating boiler according to claim 17, wherein the gas feed means in each boiler wall sector includes a gas feed unit (109-114) for the feeding of insulating gas to the surface of the boiler wall into the combustion chamber (100).
 24. Steam generating boiler according to claim 23, wherein the gas feed units (109-111; 112-114) associated with the boiler wall (103;104) are each connected to a main line (121; 122) coupled separately to the combustion gas supply (123).
 25. Steam generating boiler according to claim 24, wherein each main line (121; 122) includes a regulating element (125) for regulating the gas flow there through.
 26. Steam generating boiler according to claim 24, wherein each gas feed unit (109-114) is adapted to be selectively coupled by way of a closure element (124) to the associated main line (121; 122).
 27. Steam generating boiler according to claim 25, wherein the regulating element (125) and/or the closure element (124) is operated as a function of the volume ratios of flue gas components determined in the gas atmosphere adjoining the boiler wall.
 28. Steam generating boiler according to claim 17, wherein the burners (105, 106) are arranged for linear firing of the combustion chamber (100).
 29. Steam generating boiler according to claim 17, wherein the burners (105, 106) are arranged for tangential firing of the combustion chamber. 